I had a light bulb moment today as to why multirotor pilots who race, fly proximity, etc... usually (always?) fly rate mode instead of angle mode. Or maybe a better way to put it is, I had a light bulb moment as to why I prefer rate mode, and I think it might apply to others. I thought I would post about it, because sometimes people ask, and maybe this answer will help them.
First, definitions.
Rate mode, also known as acro mode or "manual" mode: In this mode, moving the stick causes the copter to tilt in the indicated direction. Moving the stick further from center makes the copter tilt faster. Centering the stick causes the copter to hold its current orientation.
Angle mode: In this mode, the position of the stick corresponds to a fixed angle of tilt. So moving the stick a little bit forward causes the copter to tilt a little bit forward. Moving the stick a lot forward causes the copter to tilt a lot forward. Centering the stick causes the copter to return to level. As this suggests, angle mode includes auto-level while rate mode doesn't.
Okay, so why prefer Rate mode?
Imagine that the copter is flying straight forward, tilted at a 30 degree angle (fast forward flight). If you are in rate mode, your sticks are centered. If you are in angle mode, your stick is pushed forward. Now imagine that you need to slightly adjust your trajectory to the side. Maybe there is a crosswind, or maybe you aren't quite lined up right with that hoop you're trying to fly through. In rate mode, you nudge the stick slightly to the side, then return it to center. In angle mode, you move the stick slightly to the side and keep it there.
Notice that, in rate mode, you have the advantage of the transmitter gimbal's self-centering to prevent you from accidentally pushing the stick upwards and modifying the frontward tilt of the copter. Whereas in angle mode, it is completely dependent on your muscle control not to accidentally move the stick a little bit forward or backward while you add in that little bit of sideways input. Rate mode lets you input precise trajectory adjustments to the four cardinal directions because you are always returning the sticks to center. Angle mode requires more muscle control to make precise inputs in one axis without unintentionally disturbing the copter's attitude in another axis.
Another advantage of rate mode is that the copter's orientation is unlimited. In other words, in angle mode, full stick deflection will always map to some fixed angle of tilt, and the copter will never be allowed to go past that angle. This is why you can't flip a copter in angle mode. This matters, even if you aren't intending to do flips. Let's say that you are zipping along and suddenly realize that you want to stop, IMMEDIATELY. In rate mode, you can tilt the copter completely on its butt, so that 100% of its thrust is slowing you down. In angle mode, you are going to tilt over 45 degrees, or whatever the pre-defined maximum is, and that's the end of it. Rate mode allows for more extreme and rapid changes to the copter's velocity, by allowing the copter to tilt over as far in any direction as the pilot wants. Personally, the most common place I experience this is when I am turning to fly between two obstacles, and I realize that I am about to swing wide and hit the outside obstacle. I roll further into the turn, and sometimes end up nearly 90 degrees over, punching the throttle briefly, before coming back to level to avoid hitting the ground.
MultiWii's Horizon mode addresses this limitation (and presumably other FC's have something similar) by having the FC transition from Angle mode to Rate mode as stick deflection increases. So when the sticks are near center, you're in angle mode, but if you jam them over to the side, the copter's rotation becomes unconstrained.
Finally, rate mode works better with expo settings than angle mode. I would wager that most multirotor pilots fly with some expo on their sticks. As you probably know, expo works by making the sticks less responsive (more resolution) near the center, and more responsive (less resolution) near the ends of the stick's travel. Remember that, in rate mode, the sticks always return to center except when you are inputting changes to the copter's orientation. So this means that whenever you are inputting changes, you are starting at the high-resolution part of the expo curve. With angle mode, if you are flying forward rapidly, your stick is pushed upwards and stays there, which means you are out of the high-resolution part of the expo curve. If you want to make a small change in your copter's attitude, your expo curve is going to be working against you.
First, definitions.
Rate mode, also known as acro mode or "manual" mode: In this mode, moving the stick causes the copter to tilt in the indicated direction. Moving the stick further from center makes the copter tilt faster. Centering the stick causes the copter to hold its current orientation.
Angle mode: In this mode, the position of the stick corresponds to a fixed angle of tilt. So moving the stick a little bit forward causes the copter to tilt a little bit forward. Moving the stick a lot forward causes the copter to tilt a lot forward. Centering the stick causes the copter to return to level. As this suggests, angle mode includes auto-level while rate mode doesn't.
Okay, so why prefer Rate mode?
Imagine that the copter is flying straight forward, tilted at a 30 degree angle (fast forward flight). If you are in rate mode, your sticks are centered. If you are in angle mode, your stick is pushed forward. Now imagine that you need to slightly adjust your trajectory to the side. Maybe there is a crosswind, or maybe you aren't quite lined up right with that hoop you're trying to fly through. In rate mode, you nudge the stick slightly to the side, then return it to center. In angle mode, you move the stick slightly to the side and keep it there.
Notice that, in rate mode, you have the advantage of the transmitter gimbal's self-centering to prevent you from accidentally pushing the stick upwards and modifying the frontward tilt of the copter. Whereas in angle mode, it is completely dependent on your muscle control not to accidentally move the stick a little bit forward or backward while you add in that little bit of sideways input. Rate mode lets you input precise trajectory adjustments to the four cardinal directions because you are always returning the sticks to center. Angle mode requires more muscle control to make precise inputs in one axis without unintentionally disturbing the copter's attitude in another axis.
Another advantage of rate mode is that the copter's orientation is unlimited. In other words, in angle mode, full stick deflection will always map to some fixed angle of tilt, and the copter will never be allowed to go past that angle. This is why you can't flip a copter in angle mode. This matters, even if you aren't intending to do flips. Let's say that you are zipping along and suddenly realize that you want to stop, IMMEDIATELY. In rate mode, you can tilt the copter completely on its butt, so that 100% of its thrust is slowing you down. In angle mode, you are going to tilt over 45 degrees, or whatever the pre-defined maximum is, and that's the end of it. Rate mode allows for more extreme and rapid changes to the copter's velocity, by allowing the copter to tilt over as far in any direction as the pilot wants. Personally, the most common place I experience this is when I am turning to fly between two obstacles, and I realize that I am about to swing wide and hit the outside obstacle. I roll further into the turn, and sometimes end up nearly 90 degrees over, punching the throttle briefly, before coming back to level to avoid hitting the ground.
MultiWii's Horizon mode addresses this limitation (and presumably other FC's have something similar) by having the FC transition from Angle mode to Rate mode as stick deflection increases. So when the sticks are near center, you're in angle mode, but if you jam them over to the side, the copter's rotation becomes unconstrained.
Finally, rate mode works better with expo settings than angle mode. I would wager that most multirotor pilots fly with some expo on their sticks. As you probably know, expo works by making the sticks less responsive (more resolution) near the center, and more responsive (less resolution) near the ends of the stick's travel. Remember that, in rate mode, the sticks always return to center except when you are inputting changes to the copter's orientation. So this means that whenever you are inputting changes, you are starting at the high-resolution part of the expo curve. With angle mode, if you are flying forward rapidly, your stick is pushed upwards and stays there, which means you are out of the high-resolution part of the expo curve. If you want to make a small change in your copter's attitude, your expo curve is going to be working against you.